Jakarta Mail

import jakarta.mail.*;
import jakarta.mail.internet.*;

import java.time.*;
import java.util.*;

// Send a simple, single part, text/plain e-mail
public class TestEmail {
    static Clock clock = Clock.systemUTC();
    public static void main(String[] args) {

        // SUBSTITUTE YOUR EMAIL ADDRESSES HERE!
        String to = "sendToMailAddress";
        String from = "sendFromMailAddress";
        // SUBSTITUTE YOUR ISP'S MAIL SERVER HERE!
        String host = "smtp.yourisp.invalid";

        // Create properties, get Session
        Properties props = new Properties();

        // If using static Transport.send(),
        // need to specify which host to send it to
        props.put("mail.smtp.host", host);
        // To see what is going on behind the scene
        props.put("mail.debug", "true");
        Session session = Session.getInstance(props);

        try {
            // Instantiate a message
            Message msg = new MimeMessage(session);

            //Set message attributes
            msg.setFrom(new InternetAddress(from));
            InternetAddress[] address = {new InternetAddress(to)};
            msg.setRecipients(Message.RecipientType.TO, address);
            msg.setSubject("Test E-Mail through Java");
            Date now = Date.from(LocalDateTime.now(clock).toInstant(ZoneOffset.UTC));
            msg.setSentDate(now);

            // Set message content
            msg.setText("This is a test of sending a " +
                        "plain text e-mail through Java.\n" +
                        "Here is line 2.");

            //Send the message
            Transport.send(msg);
        } catch (MessagingException mex) {
            // Prints all nested (chained) exceptions as well
            mex.printStackTrace();
        }
    }
}

package org.example;

import jakarta.activation.*;
import jakarta.mail.*;
import jakarta.mail.internet.*;

import java.io.*;
import java.time.*;
import java.util.*;

public class SendMailUsage {
    static Clock clock = Clock.systemUTC();
    public static void main(String[] args) {

        // SUBSTITUTE YOUR EMAIL ADDRESSES HERE!!!
        String to = "sendToMailAddress";
        String from = "sendFromMailAddress";
        // SUBSTITUTE YOUR ISP'S MAIL SERVER HERE!!!
        String host = "smtpserver.yourisp.invalid";

        // Create properties for the Session
        Properties props = new Properties();

        // If using static Transport.send(),
        // need to specify the mail server here
        props.put("mail.smtp.host", host);
        // To see what is going on behind the scene
        props.put("mail.debug", "true");

        // Get a session
        Session session = Session.getInstance(props);

        try {
            // Get a Transport object to send e-mail
            Transport bus = session.getTransport("smtp");

            // Connect only once here
            // Transport.send() disconnects after each send
            // Usually, no username and password is required for SMTP
            bus.connect();
            //bus.connect("smtpserver.yourisp.net", "username", "password");

            // Instantiate a message
            Message msg = new MimeMessage(session);

            // Set message attributes
            msg.setFrom(new InternetAddress(from));
            InternetAddress[] address = {new InternetAddress(to)};
            msg.setRecipients(Message.RecipientType.TO, address);
            // Parse a comma-separated list of email addresses. Be strict.
            msg.setRecipients(Message.RecipientType.CC,
                    InternetAddress.parse(to, true));
            // Parse comma/space-separated list. Cut some slack.
            msg.setRecipients(Message.RecipientType.BCC,
                    InternetAddress.parse(to, false));

            msg.setSubject("Test E-Mail through Java");
            msg.setSentDate(Date.from(LocalDateTime.now(clock).toInstant(ZoneOffset.UTC)));

            // Set message content and send
            setTextContent(msg);
            msg.saveChanges();
            bus.sendMessage(msg, address);

            setMultipartContent(msg);
            msg.saveChanges();
            bus.sendMessage(msg, address);

            setFileAsAttachment(msg, "C:/WINDOWS/CLOUD.GIF");
            msg.saveChanges();
            bus.sendMessage(msg, address);

            setHTMLContent(msg);
            msg.saveChanges();
            bus.sendMessage(msg, address);

            bus.close();

        } catch (MessagingException mex) {
            // Prints all nested (chained) exceptions as well
            mex.printStackTrace();
            // How to access nested exceptions
            while (null != mex.getNextException()) {
                // Get next exception in chain
                Exception ex = mex.getNextException();
                ex.printStackTrace();
                if (!(ex instanceof MessagingException)) break;
                else mex = (MessagingException) ex;
            }
        }
    }

    // A simple, single-part text/plain e-mail.
    public static void setTextContent(Message msg) throws MessagingException {
        // Set message content
        String mytxt = "This is a test of sending a " +
                       "plain text e-mail through Java.\n" +
                       "Here is line 2.";
        msg.setText(mytxt);

        // Alternate form
        msg.setContent(mytxt, "text/plain");

    }

    // A simple multipart/mixed e-mail. Both body parts are text/plain.
    public static void setMultipartContent(Message msg) throws MessagingException {
        // Create and fill first part
        MimeBodyPart p1 = new MimeBodyPart();
        p1.setText("This is part one of a test multipart e-mail.");

        // Create and fill second part
        MimeBodyPart p2 = new MimeBodyPart();
        // Here is how to set a charset on textual content
        p2.setText("This is the second part", "us-ascii");

        // Create the Multipart.  Add BodyParts to it.
        Multipart mp = new MimeMultipart();
        mp.addBodyPart(p1);
        mp.addBodyPart(p2);

        // Set Multipart as the message's content
        msg.setContent(mp);
    }

    // Set a file as an attachment.  Uses JAF FileDataSource.
    public static void setFileAsAttachment(Message msg, String filename)
            throws MessagingException {

        // Create and fill first part
        MimeBodyPart p1 = new MimeBodyPart();
        p1.setText("This is part one of a test multipart e-mail." +
                   "The second part is file as an attachment");

        // Create second part
        MimeBodyPart p2 = new MimeBodyPart();

        // Put a file in the second part
        FileDataSource fds = new FileDataSource(filename);
        p2.setDataHandler(new DataHandler(fds));
        p2.setFileName(fds.getName());

        // Create the Multipart.  Add BodyParts to it.
        Multipart mp = new MimeMultipart();
        mp.addBodyPart(p1);
        mp.addBodyPart(p2);

        // Set Multipart as the message's content
        msg.setContent(mp);
    }

    // Set a single part HTML content.
    // Sending data of any type is similar.
    public static void setHTMLContent(Message msg) throws MessagingException {

        String html = "<html><head><title>" +
                      msg.getSubject() +
                      "</title></head><body><h1>" +
                      msg.getSubject() +
                      "</h1><p>This is a test of sending an HTML e-mail" +
                      " through Java.</body></html>";

        // HTMLDataSource is a static nested class
        msg.setDataHandler(new DataHandler(new HTMLDataSource(html)));
    }

    /*
     * Static nested class to act as a JAF datasource to send HTML e-mail content
     */
    static class HTMLDataSource implements DataSource {
        private String html;

        public HTMLDataSource(String htmlString) {
            html = htmlString;
        }

        // Return html string in an InputStream.
        // A new stream must be returned each time.
        public InputStream getInputStream() throws IOException {
            if (null == html) throw new IOException("Null HTML");
            return new ByteArrayInputStream(html.getBytes());
        }

        public OutputStream getOutputStream() throws IOException {
            throw new IOException("This DataHandler cannot write HTML");
        }

        public String getContentType() {
            return "text/html";
        }

        public String getName() {
            return "JAF text/html dataSource to send e-mail only";
        }
    }
}